Ladder rungs



Feb, i, 1966 c. E. LARSON 3,232,373

LADDER RUNG'S Original Filed Aug. 11, 1961 2 Sheets-Sheet l ATTORNEYS C.E. LARSON LADDER RUNGS Fen l, 1966 2 Sheets-Sheet 2 Original Filed Aug.11, 1961 INVENTOR CLAYTON E. LARSON ATTORNEYS United States Patent3,232,378 LADDER RUNGS Clayton E. Larson, Brooklyn, N.Y., assignor toWhite Metal Rolling & Stamping Corporation, a corporation of New YorkContinuation of application Ser. No, 130,805, Aug. 11, 1961. Thisapplication Dec. 19, 1963, Ser. No. 333,259

2 Claims. (Cl. 182-194) This application is a continuation of mycopending application, Serial Number 130,805 filed August 11, 1961 nowabandoned.

This invention relates to ladder rungs and more particularly, itconcerns a new and improved ladder rung-tosiderail connection as well asa unique method of assembling ladder rungs and siderails havingparticular utility in ladders fabricated from light metal such asaluminum or alloys thereof.

Because of the function served by ladder, designers and manufacturesthereof have long recognized the need for a ladder construction which issufficiently strong to carry the weight of a person without danger ofthe ladder collapsing and thus causing the person to fall from aconsiderable height as well as a ladder construction which is light inweight to facilitate movement of the ladder from place to place asrequired. As a result, much use has been made by the ladder industry oflight metals such as aluminum, magnesium or alloys of one or both ofthese metals since they can be fabricated to satisfy both therequirements of strength and lightness. Yet, because of the difiicultiesencountered in working with such metals, either relatively heavysections have been employed in the past, or considerable expenses havebeen incurred in order to make possible the fabrication or joining ofthe component parts of the ladder. One of the problems encounteredheretofore which is especially troublesome with the use of light metalsin the manufacture of ladders is that of providing an adequtae non-skidor traction surface on the ladder rung and at the same time keeping theweight of the rung to a minimum without substantially increasing thecosts necessary to effect the rungto-siderail connection. For example,in the use of the well known technique of joining round, tubular-rungsto the ladder siderails by hydraulic expansion or spinning of the rungends after they have been inserted through an aperture in the siderails,it has been found that the height of flutes or serrations on theexterior of the rungs for traction or non-skid purposes must be kept towithin a maximum of 0.010 and'a flat top provided on each flute, so thatundesirable rupture of the rung end during the expansion or spinning ofprocess is prevented. To provide a desirable non-skid surface, however,the serrations or flutes for reasonable effectiveness should be at least0.020 high and be provided at their tops with sharp edges. In order,therefore, to achieve the desirable nonskid surface on the rung while atthe same time assure an effective connection of the rung to the siderailby using the technique aforementioned, the ends of the rungs necessarilymust be specially formed thereby increasing the overall cost of theladder.

Further, from the standpoint of economy in ladder manufacture, it hasbeen found desirable to attach a tubular rung to a ladder siderail byforming extending tabs at each end of the rung which tabs extend throughcorresponding apertures in the siderails and are then bent over tosecure the connection. The use of bent over tabs to secure a ladder rungto siderail connection is demonstrated to be quite old by the disclosureof US. Patent No. 901,775, of 1908. While the use of such a joint withsteel or iron alloys involves no serious difiiculties, a whollydifferent situation results when light metals such "ice as aluminum,magnesium or alloys thereof are used. The difficulty referred to isprimarily due to the relative brittleness of light metal alloys when asharp bending thereof is attempted to the extent that there is atendency for such tabs to break off thereby detracting from the use ofthis technique in the fabrication of light metal ladders. This problemis rendered more acute by the provision of flutes or serrations on therung exterior largely because of the increased thickness of materialrequired to provide the necessary depth or height of serrations, whichthickness makes more difficult the bending over of tabs extending fromsuch a rung due to the increase in stress placed in the outer fibers ofsuch a thickened section.

Accordingly, a principal object of this invention is to provide a newand improved ladder rung and connection thereof to a ladder siderail aswell as a unique method for assembling these components to achieve aladder construction by which the aforementioned problems are effectivelyand substantially overcome.

Another object of this invention is the provision of a novel ladder rungformed by extrusion of light metals such as aluminum or alloys thereof,having over that portion normally engaged by a persons foot when in use,sharp pointed serrations or flutes on the order of 0.020" to 0.025" inheight while at the same time provided with tabs which may be bent overafter insertion through apertures in a ladder siderail to secure therung-to-siderail connection.

A further object of this invention is that of providing a new andimproved ladder incorporating a rung of the type referred to and havinga rung-to-siderail connection which is resistant to loading stressesimposed on the rung and transmitted to the siderail connection thereof,while at the same time being adapted to an extremely economical andeflicient method of assembly.

Another object of this invention is the provision of a ladder having anextruded, light metal rung of semiround cross section and which isformed having an etfective non-skid or traction surface thereon withoutin any way impairing connection of the rung to the ladder siderail.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter. It should be understood, however, that the detaileddescription, while indicating preferred embodiments of the invention, isgiven by way of illustration only, since it will become apparent tothose skilled in the art from this description, that various changes andmodifications can be made without departing from the true spirit andscope of this invention.

in general, the aforementioned objects are accomplished by extruding atubular length of light metal such as aluminum or alloys thereof, toprovide a rung cross-section defining a plurality of peripherallyspaced, substantially flat wall portions integrally connected byintermediate wall portions having on the exterior thereof serrations orflutes toprovide the necessary non-skid or traction surface. Theintermediate wall portions are cut back at the ends of the rung to leaveextending the flat wall portions as siderail connecting tabs. A pair ofladder siderails are provided, each formed having sets of aperturestherein which apertures are arranged to correspond with crosssectiondefined by the connecting tabs or the flat wall portions so that thetabs may be inserted through the apertures and bent over on the outsideof the siderails to secure the rung to siderail connection. Preferably,the rungs are attached to the siderails in such a manner that the flatwail portions are positioned at the top, bottom and sides of the rungwhen the ladder is in a vertical position and further, it is preferredthat the tabs extending from .the top and .bottom flat wall portions arebent downwardly on the outside of the siderail to enhance the strengthof the connection.

A more complete understanding of the new and improved ladder of thisinvention as well as its method of assembly will be had by reference tothe accompanying drawings in which:

FIG. 1 is a perspective view illustrating one end and the upper portionof the new and improved rung of this invention;

FIG. 2 is an enlarged fragmentary side elevation of the ladder of thisinvention partially in cross-section and showing the position of theladder in use;

FIG. 3 is an enlarged fragmentary cross-sectional view taken along lines33 of FIG. 2;

FIG. 4 is a perspective view of the ladder of this invention showingdetails of the method of fabrication thereof;

FIG. 5 is an enlarged cross-sectional view taken along the lines 55 ofFIG. 4; and

FIG. 6 is a view similar to FIG. 5 taken at a later step in the process.

As shown in the drawings, the ladder of this invention includes atubular rung of an extruded, light metal alloy generally designated bythe numeral 10. Preferably, the metal from which the rung is made is analuminum alloy of the group known commercially as the 60 Series AluminumAlloys though it is contemplated that other materials having similarphysical characteristics might be used. The rung is formed havingperipherally spaced, substantially flat top, bottom and side wallportions 12, 14, and 16, respectively, extending longitudinally of therung and integrally interconnected by a plurality of intermediate wallportions 18. The intermediate wall portions 18, preferably, are ofgenerally arcuate cross-section and formed having on the exteriorthereof a plurality of longitudinally extending flutes or serrations 20.The serrations 20, as shown, are sharp pointed to assure a good non-skidor traction surface and further, are preferably 0.020" to 0.025" inheight. The fiat wall portions 12, 14, 15 and 16, on the other hand, aredevoid of such serrations, though if desired, a plurality of relativelysmall ribs 22 may be provided on the upper and lower wall portions 12and 14 respectively. The ribs 22 are of insuificient height to afford agood non-skid surface and are provided solely to avoid a perfectlysmooth surface on the upwardly facing portion of the rung as well as forappearance purposes. The height of the ribs 22, however, is desirablykept at a minimum so as not to increase the thickness of the upper andlower wall portions 14 on which they are formed.

As shown in FIG. 1, the intermediate wall portions 18 at each end of therung 1d are cut back to leave the fiat wall portions 12, 14, 15 and 16extending as siderail connecting tabs 24, 26, 28 and 30. The connectingtabs thus formed on each end of the rung provide means for effecting thejoint between the rung and ladder siderails in the assembly of theladder of this invention as will be clearly understood from thedescription which follows below.

Referring now to FIGS. 2 and 3 of the drawings, fragmentary portions ofthe ladder of this invention are shown including a pair of siderails 32and 34, each preferably, though not necessarily, formed having a centralweb portion 36 and a pair of flange portions 33. In each of the webs areformed sets of apertures 40 at points spaced longitudinally thereof asdesired for establishing the proper spacing between rungs, the apertures40 in each set being arranged to conform with the cross-sectionalconfiguration defined by the connecting tabs 24, 26, 28 and 30 or by theflat wall portions 12, 14, 15 and 16.

In the assembly of the ladder, the rungs 10 are first arranged betweenthe siderails 32 and 34 with the connecting tabs 24, 26, 28 and 30extending through the apertures 40. The loosely connected assembly thusestablished is then fed between rollers which engage the outsidesurfaces of the siderail webs 36 such that upon the advance of therollers over the siderails from top to bottom of thereof (as the ladderis ultimately to be used), both the upper and lower connecting tabs 24and 26 are bent downwardly over the exterior surface of the siderailwebs 36. The tabs 28 and 30 extending from the wall portions 15 and 16,on the other hand, are bent outwardly over the siderail web 36 as shownin FIG. 2 preferably by progressive rollers as is well known in the art.Use of progressive rollers for such bending is illustrated in prior US.patents such, .for example, as US. 2,493,415 to Navin and US. 2,825,384to Goldsmith. As an example of progressive rolling as applied to thisinvention, and with specific reference to FIGURES 4, 5 and 6 of thedrawings, the loosely assembled ladder having the rungs 10 arrangedbetween the siderails 32 and 34 and the connecting tabs 24, 26, 28 and30 extending through the apertures 40 in the siderails, is rolled in thdirection of the arrow in FIGURE 4 between oppositely disposed pairs ofrollers 46 and 48. Roller 46 is provided with a central cylindricalsurface, tapering off in beveled edges at the radial faces thereof, sothat tabs 24 and 26 are fully bent down on passage under the rollerwhile tabs 28 and 30 are bent away from each other at an angle dictatedby the angle of the roller bevel. In FIGURE 6, the second roller 48having a fully cylindrical peripheral surface flattens the tabs 28 and30 against the siderails 32 and 34 to complete the connection with therung 10. It should be obvious that, if it is required that the bendingprocess be more gradual, roller sets comprising three or more steprollers could be used in lieu of the two-step rolling process shown. Itwill be noted, therefore, that the downward bending of the upper andlower tabs 24 and 26, as well as the outward bending of the side tabs 28and 30, not only enable an extremely economical and simple method ofattaching the rungs 10 to the siderails 32 and 34, but also results in asubstantially stronger joint. This result is achieved, as will b seenparticularly in FIG. 3 of the drawings, because the tabs 24 and 26 beingbent downwardly over the outside of the siderail web, both operate toeffect a maximum resistance to separation of the rung and siderail asmight be caused by vertical loads applied to the upper portion of therung.

In use, the ladder thus assembled will, in the usual fashion, beinclined against the wall of a building or other supporting structure atan angle of the vertical approximating 15. While this angle may vary indifferent circumstances, it has been found through experience that theaforesaid angle of inclination is desirable both from the standpoint ofcomfort to one using the ladder and development of maximum strength inthe ladder siderails. Since in the assembly of the ladder the upper andlower tabs 24 and 26 and thus the upper and lower wall portions 12 and14 are arranged on the longitudinal center lin of the siderails 32 and34, the rung also, in use, assumes a canted or inclined position alongwith the siderail so that the pointed flutes or serrations 20 arepresented upwardly to be engaged by the users foot illustrated inphantom lines at 42 in FIG. 2. Because of the positioning and size ofthe serrations 20, a substantial traction or non-skid surface isatforded the user on those portions of the rung where such a tractionsurface is essential. However, because of the arrangement of theserrations 20 on the intermediate wall portions between the flat wallportions, the serrations in no way interfere with attachment of the rungto the siderail nor do they sacrifice in any respect the desirablequalities of an extruded rung of continuous crosssection. Thedifficulties encountered with the use of light metals for ladder rungsof this type, as aforementioned, are that when the rung Wallcross-section is increased sufficiently in thickness to permit anon-skid exterior surface in which serrations are provided in the rangeof 0.020" to 0.025 in height, bending or otherwise upsetting such a wallportion is for all practical purposes prevented because the increasedstresses placed in the Outer fibers of the wall result in rupturethereof and particularly along the lines defined by the bottoms of theserrations. In the present invention, however, the flat wall portions12, 14, and 16 may be kept at the maximum thickness permitted for abrupt90 bending without in any manner weakening the rung since the serrationsor flutes required to provide the necessary traction surface are omittedfrom these portions. Thus, the tabs which form extensions of these wallportions may be bent over in the manner described Without in any mannerweakening the metal and thereby afford an extremely strong and eifectivemanner of attaching the rung to the ladder siderails. Further, it is tobe noted that not all types of light metals or alloys thereof can beused in this manner because of the brittle characteristics thereof andtendency to break off when bended. For this reason, it has been foundthat certain alloys of aluminum are particularly desirable in theformation of rungs of the type to which this invention relates.Specifically, it is preferred that aluminum alloys known as the 60Series Aluminum Alloys are used though it will be understood that otheralloys having the same or similar characteristics may be used.

Thus, it will be seen that by the present invention the aforementionedobjectives are fully attained. The construction of the rung 10 asdescribed above not only brings about an extremely strong and safe rungconstruction but also the method by which it is attached to the laddersiderails enables an eifective and economical assembly of the ladderwithout in any manner sacrificing the strength and safety thereof. Theforegoing description, however, is to be understood as beingillustrative only and not limiting since it will now be apparent tothose skilled in the art that other modifications and embodiments of theinvention may be used without in any way departing from the true spiritand scope thereof as defined by the appended claims:

I claim:

1. A light metal ladder comprising:

a pair of siderails extruded from light metal comprising a flat centralweb portion and a pair of end flange portions;

a plurality of tubular rungs each extruded from light metal alloy tohave;

(a) peripherally spaced, substantially flat top, bottom and side wallportions extending longitudinally of the rung, and

(b) four intermediate arcuate wall portions integrally connected to saidflat wall portions, and

(0) four tabs on each end thereof that are straight extensions of saidflat wall portions formed by 6 removal of the arcuat wall portions fromtherebetween to the depth of said tabs;

sets of four slots through the central web portions of said siderailsarranged to conform with the cross-sectional configuration of the fourtabs of said tubular run-gs, the slots corresponding to the tabsconstituting straight extensions of said top and bottom Wall portions ofthe rungs being disposed in spaced relationship along and perpendicularto the longitudinal centerline of the side rails;

said rungs being spaced substantially equidistant along said siderailsand being fixed normal to the siderails with the ends of the arcuatewall portions of the rungs abutting the inner surfaces of the flatcentral web portions of the siderails and with the rung tabs extendingthrough said siderail slots, the tabs being bent over the outer surfacesof the flat central Web portion of the siderails securing the rung tothe siderail, the tabs which constitute straight extensions of the Wallportions of the rungs being bent over onto the outer sunfaces of thesiderail web portion, the tabs constituting straight extensions of saidtop and bottom Wall portions of the rungs, because of their disposition,absorbing the major portion of bending stresses imposed on the rungs.

2. A ladder in accordance with claim 1 wherein at least two of theopposed arcuate wall portions have longitudinal serrations at least0.020 inch deep formed in the exterior surface thereof.

References Cited by the Examiner UNITED STATES PATENTS 518,767 4/ 1894Plecker.

901,755 10/1908 Tiepolt 182-194 1,450,961 4/ 1923 Otterbeing 295132,113,403 4/ 1938 Harmon 182-228 X 2,857,665 10/1958 Cohen 295132,871,556 2/1959 Chisholm 29-513 2,957,543 10/ 1960 Larson 182228 X3,002,582 10/ 1961 Marcelis 182194 3,016,976 1/1962 Munson 182-1943,142,356 7/ 1964 Rich 182-194 FOREIGN PATENTS 561,625 10/ 1957 Belgium.

HARRISON R. MOSELEY, Primary Examiner.

REINALDO P. MACHADO, Examiner.

1. ALIGHT METAL LADDER COMPRISING: A PAIR OF SIDERAILS EXTRUDED FROM THELIGHT METAL COMPRISING A FLAT CENTRAL WEB PORTION AND A PAIR OF ENDFLANGE PORTIONS; A PLURALITY OF TUBULAR RUNGS EACH EXTRUDED FROM LIGHTMETAL ALLOY TO HAVE; (A) PERIPHERALLY SPACED, SUBSTANTIALLY FLAT TOP,BOTTOM AND SIDE WALL PORTIONS EXTENDING LONGITUDINALLY OF THE RUNG, AND(B) FOUR INTERMEDIATE ARCUATE WALL PORTION INTEGRALLY CONNECTED TO SAIDFLAT WALL PORTIONS, AND (C) FOUR TABS ON EACH END THEREOF THAT ARESTRAIGHT EXTENSIONS OF SAID FLAT WALL PORTIONS FORMED BY REMOVAL OF THEARCUATE WALL PORTIONS FROM THEREBETWEEN TO THE DEPTH OF SAID TABS; SETSOF FOUR SLOTS THROUGH THE CENTRAL WEB PORTION OF SAID SIDERAILS ARRANGEDTO CONFORM WITH THE CROSS-SECTIONAL CONFIGURATION OF THE FOUR TABS OFSAID TUBULAR RUNGS, THE SLOTS CORRESPONDING TO THE TABS CONSTITUTINGSTRAIGHT EXTENSIONS OF SAID TOP AND BOTTOM WALL PORTIONS OF THE RUNGSBEING DISPOSED IN SPACED RELATIONSHIP ALONG AND PERPENDICULAR TO THELONGITUDINAL CENTERLINE OF THE SIDE RAILS; SAID RUNGS BEING SPACEDSUBSTANTIALLY EQUIDISTANT ALONG